Cytotoxicity of a naturally occuring spirostanol saponin, progenin III, towards a broad range of cancer cell lines by induction of apoptosis, autophagy and necroptosis

Advances in antitumor activity and mechanism of natural steroidal saponins: A review of advances, challenges, and future prospects

BACKGROUND

Cancer, the second leading cause of death worldwide following cardiovascular diseases, presents a formidable challenge in clinical settings due to the extensive toxic side effects associated with primary chemotherapy drugs employed for cancer treatment. Furthermore, the emergence of drug resistance against specific chemotherapeutic agents has further complicated the situation. Consequently, there exists an urgent imperative to investigate novel anticancer drugs. Steroidal saponins, a class of natural compounds, have demonstrated notable antitumor efficacy. Nonetheless, their translation into clinical applications has remained unrealized thus far. In light of this, we conducted a comprehensive systematic review elucidating the antitumor activity, underlying mechanisms, and inherent limitations of steroidal saponins. Additionally, we propose a series of strategic approaches and recommendations to augment the antitumor potential of steroidal saponin compounds, thereby offering prospective insights for their eventual clinical implementation.

PURPOSE

This review summarizes steroidal saponins' antitumor activity, mechanisms, and limitations.

METHODS

The data included in this review are sourced from authoritative databases such as PubMed, Web of Science, ScienceDirect, and others.

RESULTS

A comprehensive summary of over 40 steroidal saponin compounds with proven antitumor activity, including their applicable tumor types and structural characteristics, has been compiled. These steroidal saponins can be primarily classified into five categories: spirostanol, isospirostanol, furostanol, steroidal alkaloids, and cholestanol. The isospirostanol and cholestanol saponins are found to have more potent antitumor activity. The primary antitumor mechanisms of these saponins include tumor cell apoptosis, autophagy induction, inhibition of tumor migration, overcoming drug resistance, and cell cycle arrest. However, steroidal saponins have limitations, such as higher cytotoxicity and lower bioavailability. Furthermore, strategies to address these drawbacks have been proposed.

CONCLUSION

In summary, isospirostanol and cholestanol steroidal saponins demonstrate notable antitumor activity and different structural categories of steroidal saponins exhibit variations in their antitumor signaling pathways. However, the clinical application of steroidal saponins in cancer treatment still faces limitations, and further research and development are necessary to advance their potential in tumor therapy.

Cytotoxicity, acute and sub-chronic toxicities of the leaves of Bauhinia thonningii (Schumach.) Milne-Redh. (Caesalpiniaceae)

BACKGROUND

Bauhinia thonningii is a plant traditionally used against many human diseases such as gastric ulcers, fever, inflammations, coughs, dysentery, diarrhea, and malaria. In the present investigation, the cytotoxicity of methanol extract of Bauhinia thonningii leaves (BTL), fractions and the isolated phytoconstituents was determined in a panel of 9 human cancer cell lines including drug sensitive and multidrug-resistant (MDR) phenotypes. The acute and sub-chronic oral toxicity of BTL was investigated as well.

METHODS

Compounds were isolated using chromatographic techniques while their chemical structures were determined using spectroscopic methods. The resazurin reduction assay (RRA) was used to evaluate the cytotoxicity of samples, propidium iodide (PI) for apoptosis, 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide (JC-1) staining for mitochondrial membrane potential (MMP) analysis, 2´,7´-dichlorodihydrofluoresceine diacetate (H2DCFH-DA) staining for the quantification of reactive oxygen species (ROS), whereas Caspase Glo assays were combined by means of flow cytometry. Furthermore, the toxicological investigations were performed as recommended by the Organization for Economic Cooperation and Development (OECD).

RESULTS

The botanicals as well as 6-C-methylquercetin-3,7-dimethyl ether (2), quercetin-3-O-L-rhamnopyranoside (5), quercetin-3-O-β-glucopyranoside (6), 6,8-C-dimethylkaempferol 3,7-dimethyl ether (7), and 6,8-C-dimethylkaempferol-3-methyl ether (8) had promising cytotoxic effects in the 9 tested cancer cell lines. The IC50 values below 20 µg/mL (botanicals) or 10 µM (compounds) on at least 1/9 tested cancer cell lines were considered. The best cytotoxic effects with IC50 values below 5 µM were achieved with compounds 7 against CEM/ADR5000 leukemia cells (2.86 µM) and MDA-MB-231-pcDNA breast adenocarcinoma cells (1.93 µM) as well as 8 against CCRF-CEM leukemia cells (3.03 µM), CEM/ADR5000 cells (2.42 µM), MDA-MB-231-pcDNA (2.34 µM), and HCT116 p53-/- cells (3.41 µM). BTL and compound 8 induced apoptotic cell death in CCRF-CEM cells through caspase activation, alteration of MMP, and increased ROS production. BTL did not cause any adverse effects in rats after a single administration at 5000 mg/kg or a repeated dose of 250 mg/kg body weight (b. w.).

CONCLUSION

Bauhinia thonningii and its constituents are sources of cytotoxic drugs that deserve more in-depth studies to develop novel antiproliferative phytomedicine to fight cancer including resistant phenotypes.

Harnessing the Potential of Non-Apoptotic Cell Death Processes in the Treatment of Drug-Resistant Melanoma

Melanoma is a highly malignant skin cancer that is known for its resistance to treatments. In recent years, there has been significant progress in the study of non-apoptotic cell death, such as pyroptosis, ferroptosis, necroptosis, and cuproptosis. This review provides an overview of the mechanisms and signaling pathways involved in non-apoptotic cell death in melanoma. This article explores the interplay between various forms of cell death, including pyroptosis, necroptosis, ferroptosis, and cuproptosis, as well as apoptosis and autophagy. Importantly, we discuss how these non-apoptotic cell deaths could be targeted as a promising therapeutic strategy for the treatment of drug-resistant melanoma. This review provides a comprehensive overview of non-apoptotic processes and gathers recent experimental evidence that will guide future research and eventually the creation of treatment strategies to combat drug resistance in melanoma.

Cytotoxicity of the methanol extracts and compounds of Brucea antidysenterica (Simaroubaceae) towards multifactorial drug-resistant human cancer cell lines

BACKGROUND

Cancer remains a global health concern and constitutes an important barrier to increasing life expectancy. Malignant cells rapidly develop drug resistance leading to many clinical therapeutic failures. The importance of medicinal plants as an alternative to classical drug discovery to fight cancer is well known. Brucea antidysenterica is an African medicinal plant traditionally used to treat cancer, dysentery, malaria, diarrhea, stomach aches, helminthic infections, fever, and asthma. The present work was designed to identify the cytotoxic constituents of Brucea antidysenterica on a broad range of cancer cell lines and to demonstrate the mode of induction of apoptosis of the most active samples.

METHODS

Seven phytochemicals were isolated from the leaves (BAL) and stem (BAS) extract of Brucea antidysenterica by column chromatography and structurally elucidated using spectroscopic techniques. The antiproliferative effects of the crude extracts and compounds against 9 human cancer cell lines were evaluated by the resazurin reduction assay (RRA). The activity in cell lines was assessed by the Caspase-Glo assay. The cell cycle distribution, apoptosis via propidium iodide (PI) staining, mitochondrial membrane potential (MMP) through 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide (JC-1) staining, and the reactive oxygen species (ROS) via 2´,7´-dichlorodihydrofluoresceine diacetate (H2DCFH-DA) staining, were investigated by flow cytometry.

RESULTS

Phytochemical studies of the botanicals (BAL and BAS) led to the isolation of seven compounds. BAL and its constituents 3, (3-(3-Methyl-1-oxo-2-butenyl))1H indole (1) and hydnocarpin (2), as well as the reference compound, doxorubicin, had antiproliferative activity against 9 cancer cell lines. The IC₅₀ values varied from 17.42 µg/mL (against CCRF-CEM leukemia cells) to 38.70 µg/mL (against HCT116 p53^-/- colon adenocarcinoma cells) for BAL, from 19.11 µM (against CCRF-CEM cells) to 47.50 µM (against MDA-MB-231-BCRP adenocarcinoma cells) for compound 1, and from 4.07 µM (against MDA-MB-231-pcDNA cells) to 11.44 µM (against HCT116 p53^+/+ cells) for compound 2. Interestingly, hypersensitivity of resistant cancer cells to compound 2 was also observed. BAL and hydnocarpin induced apoptosis in CCRF-CEM cells mediated by caspase activation, the alteration of MMP, and increased ROS levels.

CONCLUSION

BAL and its constituents, mostly compound 2, are potential antiproliferative products from Brucea antidysenterica. Other studies will be necessary in the perspective of the discovery of new antiproliferative agents to fight against resistance to anticancer drugs.

Targeting regulated cell death with plant natural compounds for cancer therapy: A revisited review of apoptosis, autophagy-dependent cell death, and necroptosis

Regulated cell death (RCD) refers to programmed cell death regulated by various protein molecules, such as apoptosis, autophagy-dependent cell death, and necroptosis. Accumulating evidence has recently revealed that RCD subroutines have several links to many types of human cancer; therefore, targeting RCD with pharmacological small-molecule compounds would be a promising therapeutic strategy. Moreover, plant natural compounds, small-molecule compounds synthesized from plant sources, and their derivatives have been widely reported to regulate different RCD subroutines to improve potential cancer therapy. Thus, in this review, we focus on updating the intricate mechanisms of apoptosis, autophagy-dependent cell death, and necroptosis in cancer. Moreover, we further discuss several representative plant natural compounds and their derivatives that regulate the above-mentioned three subroutines of RCD, and their potential as candidate small-molecule drugs for the future cancer treatment.

Cytotoxicity, acute and sub-chronic toxicities of the fruit extract of Tetrapleura tetraptera (Schumm. & Thonn.) Taub. (Fabaceae)

Background

Tetrapleura tetraptera is a medicinal spice traditionally used to treat cancer, diabetes, and several other ailments. This study analyzed the cytotoxicity of the dichloromethane methanol extract of T. tetraptera fruits (TTF) and its constituents. The toxicity profile of the TTF extract was also evaluated in rats.

Methods

The Cytotoxicity of this extract was evaluated using the resazurin reduction assay (RRA). Acute and sub-chronic toxicity studies were performed according to the protocol described by the Organisation for Economic Cooperation, and Development (OECD). Hematological, serum, and urine biochemical parameters, as well as histological sections of the liver and kidney, were also evaluated based on standard methods.

Results

The TTF extract, compound 5, and the reference drug doxorubicin were active in all 9 tested cancer cell lines. The recorded IC₅₀ ranged from 18.32 μM (against B16-F1 murine melanoma cells) to 36.18 μM (against SKMel-505 BRAF wildtype melanoma cells) for TTF, from 10.02 μM (towards MaMel-80a BRAF-V600E homozygous mutant melanoma cells) to 31.73 μM (against SKMel-28 BRAF-V600E homozygous mutant melanoma cells) for compound 5, and from 0.22 μM (against B16-F1 cells) to 9.39 μM (against SKMel-505 cells) for doxorubicin. The study of acute toxicity test showed that the lethal dose (LD₅₀) of this extract was greater than 5000 mg/kg body weight. In the sub-chronic toxicity studies, variations were observed in some biochemical parameters, especially at higher doses.

Conclusion

TTF and its most active compound (5) are found to be potential cytotoxic agents, meanwhile, TTF was safe when given a single oral dose of 5000 mg/kg. However, caution is necessary in case of prolonged oral administration due to potential alterations of renal function at high doses (> 1000 mg/kg).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-022-03659-1.

Naturally occurring steroidal saponins as potential anticancer agents: Current developments and mechanisms of action

Cancer is claimed as a prevalent cause of mortality throughout the world. Conventional chemotherapy plays a pivotal role in the treatment of cancers, but the multidrug resistance has already become one of the major impediments for efficacious cancer therapy, creating a great demand for the development of novel anticancer drugs. Steroidal saponins, abundantly found in nature, possess extensive structural variability, and some naturally occurring steroidal saponins exhibited profound anticancer properties through a variety of pathways. Hence, naturally occurring steroidal saponins are powerful lead compounds/candidates in the development of novel therapeutic agents. This review article described the recent progress in naturally occurring steroidal saponins as potential anticancer agents, and the mechanisms of action were also discussed, covering articles published between 2017 and 2021.

Botanical from the Fruits Mesocarp of Raphia vinifera Displays Antiproliferative Activity and Is Harmless as Evidenced by Toxicological Assessments

Raphia vinifera is widely used to treat several diseases including digestive disorders, dysentery, and genitourinary infections. In this study, the mineral contents, the cytotoxicity, and the toxicological effect of the crude CHCl3/MeOH extract (RVM) from the mesocarp of Raphia vinifera were evaluated. The mineral contents were evaluated using the method described by the Association of Official Analytical Chemists (AOAC). The cytotoxicity of both extract and chemical compounds from the plants was determined by a resazurin reduction assay (RRA). The toxicological studies were carried out using the experimental procedure of the Organization for Economic Cooperation and Development (OECD). After killing the rats, biochemical, histopathological, and hematological studies were performed. The result indicated that RVM is rich in zinc (6.52 mg/100 g of DM) and sodium (194.5 mg/100 g of DM). RVM had a cytotoxicity effect with IC50 values lower than 30 μg/mL in 18/18 cancer cell lines tested. These recorded IC50 values were between 12.35 µg/mL (toward CCRF-CEM leukemia cells) and 26.66 µg/mL (toward SKMel-505 BRAF wild-type melanoma cells). Raphvinin 4 displayed good cytotoxicity against MaMel-80aBRAF-V600E homozygous mutant with the IC50 of 10.42 μM. RVM was relatively nontoxic to rats, the median lethal dose (DL50) being above 5000 mg/kg body weight. However, during the oral administration period extending for 28 days, precautions should be taken due to the increase in urinary creatinine level and decrease in spleen weight in the male rats given the highest dose (1000 mg/kg) of extract. Conclusively, the extract of Raphia vinifera is weakly toxic in rats and could be further used in the development of anticancer phytomedicines.

Current perspectives on naturally occurring saponins as anticancer agents

Saponins, a heterogeneous group of sterol and triterpene glycosides, are distributed widely in nature. Naturally occurring saponins could act on diverse targets in cancer cells and consequently exert potential antiproliferative effects in various cancers, including drug-resistant forms. Therefore, naturally occurring saponins are useful templates for the discovery of novel anticancer candidates. Covering articles published between January 2020 and October 2021, this review aims to outline the recent development of naturally occurring steroidal and triterpenoidal saponins with anticancer potential to provide novel anticancer lead hits/candidates.

Conversion of Dioscorea zingiberensis saponins to prosapogenin A by enzymatic hydrolysis

Prosapogenin A is a secondary saponin in Dioscorea zingiberensis, and it showed remarkable pharmacological effects. Due to very low content and lack of well-developed biotransformation, its preparation was not efficient and clean. This study aims to establish an eco-friendly strategy for preparation of Prosapogenin A from plant material. Physical separation was employed to recycle starch and cellulose, and then D101 resin and polyamide packed-bed column was incorporated for purification of total steroidal saponins (TSS). After these pretreatments, purity of TSS was largely increased to 83.2% with recovery at 87.6%, which was subjected to enzymatic hydrolysis. Optimized reaction system was constructed in 0.20 M HAc-NaAc buffer (pH4.2) containing cellulase/TSS (3:1, w/w), and the hydrolysis was performed at 53 °C for 6 h. Consequently, TSS was almost completely hydrolyzed to Prosapogenin A, while the highest yield reached 5.62%. The newly proposed approach is promising for efficient preparation of Prosapogenin A in industrial applications.

Identification and Characterization of a Trillin Rhamnosyltransferase From Dioscorea zingiberensis

Dioscorea zingiberensis accumulates abundant steroidal saponins, such as dioscin, which is the principal bioactive ingredient displaying a wide range of pharmacological activities. Diosgenin is the aglycone of dioscin, and recently, genes encoding cytochrome P450 enzymes in the late steps of diosgenin biosynthesis have been isolated. Diosgenin was successfully synthesized in the cholesterol-producing yeasts. From diosgenin to dioscin, one glucose and two rhamnose groups need to be added. Although genes encoding UDP-glucosyltransferases converting diosgenin to trillin were isolated, genes encoding UDP-rhamnosyltransferases involved in dioscin biosynthesis remain unknown. In this study, we isolated the cDNA encoding the trillin rhamnosyltransferase (designated DzGT1) from D. zingiberensis. Heterologous expression of DzGT1 in Escherichia coli cells showed that the gene product exhibits an enzyme activity that glycosylates the trillin to form prosapogenin A of dioscin (PSA). The transcript level of DzGT1 is in accord with PSA accumulation in different organs of D. zingiberensis. Integration of the biochemical, metabolic, and transcriptional data supported the function of DzGT1 in dioscin biosynthesis. The identification and characterization of DzGT1 will help understand the metabolism of steroidal saponins in D. zingiberensis and provide candidate UDP-rhamnosyltransferase for efficient production of PSA, dioscin, and relevant steroidal saponins in microbial hosts.

Saponins in Cancer Treatment: Current Progress and Future Prospects

Saponins are steroidal or triterpenoid glycoside that is distinguished by the soap-forming nature. Different saponins have been characterized and purified and are gaining attention in cancer chemotherapy. Saponins possess high structural diversity, which is linked to the anticancer activities. Several studies have reported the role of saponins in cancer and the mechanism of actions, including cell-cycle arrest, antioxidant activity, cellular invasion inhibition, induction of apoptosis and autophagy. Despite the extensive research and significant anticancer effects of saponins, there are currently no known FDA-approved saponin-based anticancer drugs. This can be attributed to a number of limitations, including toxicities and drug-likeness properties. Recent studies have explored options such as combination therapy and drug delivery systems to ensure increased efficacy and decreased toxicity in saponin. This review discusses the current knowledge on different saponins, their anticancer activity and mechanisms of action, as well as promising research within the last two decades and recommendations for future studies.

Bioactivity of fractions and constituents of Piper capense fruits towards a broad panel of cancer cells

ETHNOPHARMACOLOGICAL RELEVANCE

Piper capense is a medicinal spice whose fruits are traditionally used as aqueous decoction to heal several ailments such as trypanosomiasis, helminthic infections, and cancer.

AIM OF THE STUDY

(1) To perform phytochemical investigation of the methanol extract of Piper capense; (2) to evaluate the cytotoxicity of botanicals (PCF, fractions PCFa-e), isolated phytochemicals on a broad panel of animal and human cancer cell lines; (3) to evaluate the induction of apoptosis of the most active samples.

MATERIAL AND METHODS

Resazurin reduction assay (RRA) was used to determine the cytotoxicity of the studied samples. Cell cycle distribution (PI staining), apoptosis (annexin V/PI staining), mitochondrial membrane potential (MMP; JC-1) and reactive oxygen species (ROS; H₂DCFH-DA) were measured by flow cytometry. Column chromatography (CC) was used for the purification of PCF, whilst nuclear magnetic resonance (NMR) spectroscopic and mass spectrometric (MS) analyses were applied for structural elucidation.

RESULTS

The phytochemical investigation of PCF led to the isolation of 11 compounds: licarin B (1), licarin A (2), 7-(1,3-benzodioxol-5-yl)-7,8-dihydro-8-methyl-5-(2-propenyl)-furo[3,2-e]-1,3-benzodioxole (3), nitidine isocyanate (4), 5-hydroxy-7,4'-dimethoxyflavone (5), cardamomin (6), sitosterol (7) and stigmasterol (8), β-sitosterol 3-O-β-_D-glucopyranoside (9), oleanolic acid (10) and lupeol (11). Fraction PCFb, compound 2 and doxorubicin (as positive control drug) revealed cytotoxic effects towards the 18 tested cancer cell lines. The IC₅₀ values ranged from 6.1 μg/mL (against CCRF-CEM cells) to 44.2 μg/mL (against BRAF-V600E homozygous mutant melanoma cells) for PSCb; from 4.3 μM (against CCRF-CEM cells) to 21.8 μM (against HCT116 p53^-/-) for compound 2 and from 0.02 μM (against CCRF-CEM cells) to 123.0 μM (against CEM/ADR5000 cells) for doxorubicin. PCFb and compound 2 induced apoptosis in CCRF-CEM cells mediated by activation of caspase 3/7, 8 and 9, MMP alteration and increased ROS production.

CONCLUSION

Piper capense is a source of potent cytotoxic botanicals and phytochemicals that could help to fight various types of cancer including multidrug resistance phenotypes. PCFb and compound 2 should further be explored to develop new drugs to fight malignancies.

Cytotoxicity of Quillaja saponaria Saponins towards Lung Cells Is Higher for Cholesterol-Rich Cells

The purpose of the study was to compare cytotoxicity of two Quillaja saponaria bark saponin (QBS) mixtures against two lung cell lines: normal MRC-5 fibroblast cell line and tumor A-549 epithelial cells of lungs’ alveoli. The study, performed both at a macro-scale and in a dedicated microfluidic device, showed that QBS was more toxic to the cell line more abundant in cholesterol (MRC-5). The QBS mixture with higher saponin fraction was found to be more cytotoxic towards both cell lines. The results may help to better understand the cytotoxicity of saponin-rich herbal medicines towards normal and tumor cells depending on their cholesterol content.

Cytotoxicity of botanicals and isolated phytochemicals from Araliopsis soyauxii Engl. (Rutaceae) towards a panel of human cancer cells

ETHNOPHARMACOLOGICAL RELEVANCE

Araliopsis soyauxii Engl. (Rutaceae) is a Cameroonian medicinal plant traditionally used to treat lung diseases, malaria, and gonorrhea. It has been demonstrated that infectious disease contribute to about 20% of all human tumours.

AIMS OF THE STUDY

(1) To perform a phytochemical investigation of the dichloromethane-methanol 1:1 extracts of the bark (ASB), roots (ASR), and leaves (ASL) from Araliopsis soyauxii; (2) to evaluate the cytotoxicity of extracts and isolated compounds; (3) to determine the mode of induction of apoptosis of ASB and kihadanin B (12).

MATERIALS AND METHODS

Fourteen constituents of the crude extracts were isolated by column chromatography, while spectroscopic techniques were used for structural elucidation. The resazurin reduction assay (RRA) was applied to determine the cytotoxicity of samples towards a panel of 9 cancer cell lines. For caspases activity, the Caspase-Glo assay was used; flow cytometry was applied to investigate the cell cycle distribution (PI staining), apoptosis (annexin V/PI staining), mitochondrial membrane potential (MMP; JC-1 staining), and the reactive oxygen species (ROS; H₂DCFH-DA staining).

RESULTS

Phytochemical investigations of botanicals (ASB, ASR, and ASL) led to the isolation of 14 compounds. Extract ASB, obacunone (11), kihadanin B (12) as well as doxorubicin (control drug) revealed cytotoxicity towards the 9 cancer cell lines tested. The IC₅₀ values ranged from 11.11 μg/mL (against CCRF-CEM leukemia cells) to 28.18 μg/mL (against HCT116 p53^+/+ colon adenocarcinoma cells) for ASB; from 28.25 μM (against MDA-MB-231-pcDNA breast adenocarcinoma cells) to 65.13 μM (against HepG2 hepatocarcinoma cells) for compound 11, and from 5.77 μM (against CCRF-CEM cells) to 43.56 μM (against U87.MGΔEGFR glioblastoma cells) for compound 12. ASB and compound 12 induced apoptosis in CCRF-CEM cells. ASB induced the apoptotic process mediated by MMP alteration and enhanced ROS production, while compound 12 induced apoptosis by caspases activation, MMP alteration, and enhanced ROS production.

CONCLUSION

This study demonstrated that Araliopsis soyauxii is a potential source of cytotoxic phytochemicals such as kihadanin B and that ASB and compound 12. Extract and compounds will be explored further to develop anticancer drugs.

Targeting autophagy using saponins as a therapeutic and preventive strategy against human diseases

Autophagy is a ubiquitous mechanism for maintaining cellular homeostasis through the degradation of long-lived proteins, insoluble protein aggregates, and superfluous or damaged organelles. Dysfunctional autophagy is observed in a variety of human diseases. With advanced research into the role that autophagy plays in physiological and pathological conditions, targeting autophagy is becoming a novel tactic for disease management. Saponins are naturally occurring glycosides containing triterpenoids or steroidal sapogenins as aglycones, and some saponins are reported to modulate autophagy. Research suggests that saponins may have therapeutic and preventive efficacy against many autophagy-related diseases. Therefore, this review comprehensively summarizes and discusses the reported saponins that exhibit autophagy regulating activities. In addition, the relevant signaling pathways that the mechanisms involved in regulating autophagy and the targeted diseases were also discussed. By regulating autophagy and related pathways, saponins exhibit bioactivities against cancer, neurodegenerative diseases, atherosclerosis and other cardiac diseases, kidney diseases, liver diseases, acute pancreatitis, and osteoporosis. This review provides an overview of the autophagy-regulating activity of saponins, the underlying mechanisms and potential applications for managing various diseases.

Natural Products as Inducers of Non-Canonical Cell Death: A Weapon against Cancer

Simple Summary

Anticancer therapeutic approaches based solely on apoptosis induction are often unsuccessful due to the activation of resistance mechanisms. The identification and characterization of compounds capable of triggering non-apoptotic, also called non-canonical cell death pathways, could represent an important strategy that may integrate or offer alternative approaches to the current anticancer therapies. In this review, we critically discuss the promotion of ferroptosis, necroptosis, and pyroptosis by natural compounds as a new anticancer strategy.

Abstract

Apoptosis has been considered the main mechanism induced by cancer chemotherapeutic drugs for a long time. This paradigm is currently evolving and changing, as increasing evidence pointed out that antitumor agents could trigger various non-canonical or non-apoptotic cell death types. A considerable number of antitumor drugs derive from natural sources, both in their naturally occurring form or as synthetic derivatives. Therefore, it is not surprising that several natural compounds have been explored for their ability to induce non-canonical cell death. The aim of this review is to highlight the potential antitumor effects of natural products as ferroptosis, necroptosis, or pyroptosis inducers. Natural products have proven to be promising non-canonical cell death inducers, capable of overcoming cancer cells resistance to apoptosis. However, as discussed in this review, they often lack a full characterization of their antitumor activity together with an in-depth investigation of their toxicological profile.

The alkaloid, soyauxinium chloride, displays remarkable cytotoxic effects towards a panel of cancer cells, inducing apoptosis, ferroptosis and necroptosis

The cytotoxic potential of a naturally occurring indoloquinazoline alkaloid, soyauxinium chloride (SCHL), was determined on a broad panel of animal and human cancer cell lines, including various sensitive and drug-resistant phenotypes. The cytotoxicity, SCHL-induced autophagic, ferroptotic, and necroptotic cell death were evaluated by the resazurin reduction assay (RRA). Caspase-Glo assay was used to detect the activity of caspases using spectrophotometric analysis. Flow cytometry was applied for cell cycle analysis (PI staining), apoptosis (annexin V/PI staining), mitochondrial membrane potential (MMP) (JC-1) and reactive oxygen species (ROS) (H₂DCFH-DA). SCHL and doxorubicin (reference molecule) exhibited cytotoxic effects towards the 18 cancer cell lines tested. The IC₅₀ values obtained ranged from 3.64 μM (towards CCRF-CEM leukemia cells) to 16.86 μM (against the BRAF-wildtype SKMel-505 melanoma cells for SCHL). Collateral sensitivity of the resistant HCT116 p53^-/- colon adenocarcinoma cells to SCHL was observed as well as the normal sensitivity of CEM/ADR5000 leukemia cells, MDA-MB-231-BCRP breast adenocarcinoma cells and U87. MGΔEGFR glioblastoma cells. SCHL induced apoptosis in CCRF-CEM cells via caspases 3/7-, 8- and 9-activation, MMP alteration and increased ROS production, and otherwise ferroptosis and necroptosis. SCHL is a prominent cytotoxic alkaloid that should be further studied to develop a novel drug to combat cancers including refractory phenotypes.

Steroidal saponins from Raphia vinifera and their cytotoxic activity

Phytochemical analysis of the fruits of Raphia vinifera led to the isolation of four new steroidal saponins (1-4), along with six known secondary metabolites (6-10). The structures of the isolated compounds were determined based on the analyses of NMR and mass spectrometric data, and chemical degradation reactions. Among the compounds tested, 1 and 4 showed the most promising cytotoxic activity against the drug-sensitive CCRF-CEM leukemia cell lines, with IC₅₀ values of 3.55 µM and 7.14 µM, respectively.

Synthesis and Pharmacological Effects of Diosgenin-Betulinic Acid Conjugates

The target diosgenin–betulinic acid conjugates are reported to investigate their ability to enhance and modify the pharmacological effects of their components. The detailed synthetic procedure that includes copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition (click reaction), and palladium-catalyzed debenzylation by hydrogenolysis is described together with the results of cytotoxicity screening tests. Palladium-catalyzed debenzylation reaction of benzyl ester intermediates was the key step in this synthetic procedure due to the simultaneous presence of a 1,4-disubstituted 1,2,3-triazole ring in the molecule that was a competing coordination site for the palladium catalyst. High pressure (130 kPa) palladium-catalyzed procedure represented a successful synthetic step yielding the required products. The conjugate 7 showed selective cytotoxicity in human T-lymphoblastic leukemia (CEM) cancer cells (IC₅₀ = 6.5 ± 1.1 µM), in contrast to the conjugate 8 showing no cytotoxicity, and diosgenin (1), an adaptogen, for which a potential to be active on central nervous system was calculated in silico. In addition, 5 showed medium multifarious cytotoxicity in human T-lymphoblastic leukemia (CEM), human cervical cancer (HeLa), and human colon cancer (HCT 116). Betulinic acid (2) and the intermediates 3 and 4 showed no cytotoxicity in the tested cancer cell lines. The experimental data obtained are supplemented by and compared with the in silico calculated physico-chemical and absorption, distribution, metabolism, and excretion (ADME) parameters of these compounds.